Prior art semiconductor-based pressure sensors generally make use of a structure comprising four silicon gauges disposed in a Wheatstone bridge, and deliberately doped with acceptor impurities so as to have P type conductivity, such gauges being made by diffusing or implanting impurities in a silicon substrate having N type conductivity.
The effect made use of is piezoresistivity which shows up in the electrical resistance of each gauge varying as a function of the stress to which the gauge is subjected by pressure being applied thereto.
Since the resistivity of silicon is sensitive only to single-axis and to two-axis stresses, it is not directly sensitive to hydrostatic pressure, so sensors of this type are designed in such a manner that the application of a hydrostatic pressure gives rise to the appearance of such stresses. To do this, such a sensor includes a membrane made by etching one of its faces, which face is subjected to a reference pressure, while the other face supporting the strain gauges is subjected to the hydrostatic pressure to be measured in such a manner as to ensure that on said face, there appears a system of stresses that are directed mainly in the plane of the membrane.
By suitably selecting the positions of the gauges relative to said system of stresses, the electrical resistance of two of the gauges will increase with applied pressure while the electrical resistance of the other two decreases. The Wheatstone bridge is thus taken out of balance and a signal can thus be obtained which depends on the pressure.
Although the properties of such sensors are quite satisfactory in numerous applications, they nevertheless suffer from limitations that are detrimental to their use in certain particular cases, some of which cases are important.
In particular, not only is the signal delivered by sensors of this type intrinsically representative both of pressure and of temperature, but it always turns out to be extremely difficult to provide proper temperature correction for such a signal representative of pressure and of temperature.
In addition, all such sensors manifest the problems inherent to composite structures, in particular problems of long term stability and of hysteresis.
Proposals have already been made in patent Document FR-A-2 629 640 by the present Assignee to remedy these drawbacks by providing a temperature-correcting hydrostatic pressure transducer making use of a pressure-sensitive layer constituted by a ternary material made up of elements taken from columns III and V of the periodic table and grown epitaxially on a binary substrate of III-V material, said transducer further including a temperature sensor supported on the same substrate and suitable for providing a signal representative of the temperature thereof. In a particular embodiment, this temperature sensor also includes a semiconductor layer of III-V ternary material overlying the pressure-sensitive layer and separated therefrom by an insulating layer of III-V ternary material.
That transducer provides improvements over sensors having silicon piezoresistive gauges.
An object of the present invention is to provide a novel III-V material monolithic transducer serving, in particular, to provide electrical signals that are a function of the hydrostatic pressure and the temperature of the medium surrounding the transducer.